Delay Application.LoadLevel

Hello! I was trying to make main menu for my game. I wanted to have sound when clicking "start game" button, but when I use yield WaitForSeconds (3); my sound is playing after those 3 seconds, and it plays for only about half a second and then the level loads. I want this sound playing immediately after pressing the button. I was wondering if anybody can help me. Here's my main menu script:

 var isQuit=false;
 var hoverSound : AudioClip;
 var clickSound : AudioClip;
 var levelNumber : int;
 
 function OnMouseEnter(){
   GetComponent.().material.color=Color.red;
   GetComponent.().PlayOneShot(hoverSound);
 }
 
 function OnMouseExit(){
   GetComponent.().material.color=Color.white;
 }
 
 function OnMouseUp(){
 
   if (isQuit==true) {
 
     Application.Quit();
   }
   else{
 
     yield WaitForSeconds (3)
     Application.LoadLevel(levelNumber);
     GetComponent.().PlayOneShot(clickSound);
   }
 }
 
 function Update(){
 
   if (Input.GetKey(KeyCode.Escape)) { 
    Application.Quit();
   }
 }

Sorry for my bad english :D